1. Field of the Invention
This invention relates to machine elements and mechanisms generally, but more particularly to gear casings.
2. Description of the Related Art
The incorporation of an electric motor gearbox into a mechanical vending machine for the purpose of delivering a desired product to a purchaser is a well-known concept. An early example of such a vending machine is shown in U.S. Pat. No. 2,497,219 which issued to Joseph Haumann on Feb. 14, 1950.
However, early vending machines, such as the one patented by Haumann, did not permit the purchaser to view the product before coins were deposited. Also, the choice of products sold in such early vending machines was limited to one or a few items.
Eventually, these early vending machines were replaced by so-called "glass-fronted" machines 10, one of which is shown in FIG. 1. These glass-fronted machines 10 are still in use and are popular with consumers because items for sale can be viewed and also because of the variety of choices offered. For example, the so-called "Snack Center" machine manufactured by Crane National Vendors of Bridgeton, Missouri, holds up to 53 selections and 1,100 individual items in all.
As shown in FIG. 2, each machine 10 has a plurality of shelves 12 which individually slide out for loading and unloading by service personnel. Each shelf 12 has a plurality of columns 14 separated by dividers 16 that serve to segregate different items to be sold. At the rear of each shelf 12, there is a portion 18 reserved for a plurality of electric motor gearboxes (not shown in FIG. 2, but see FIGS. 3 and 4). In FIG. 3, a prior art motor 20P is illustrated and has four main parts: a gearbox housing 26, a miniature motor (hereinafter "minimotor") 22, a printed circuit (hereinafter "PC") board 24, and an assembly of gears inside the gearbox housing 26.
Returning to FIG. 2, it can be seen that the deposit of coins in a slot 28 and the pushing of selection buttons 30 activate the electric motor gearbox 20P for a column 14 so that a spiral 32 turns in the direction of an arrow A until the selected item I (not shown in FIG. 2, but see FIG. 1) is moved forwardly and the item I reaches a front edge 12E of the shelf 12.
Returning to FIG. 1, it can be seen that the item I has reached the edge 12E of the shelf 12. Ordinarily, the item I will be dropped over the edge 12E and will fall down into a space having a door 34 through which the purchaser reaches to take out the item I.
Unfortunately, in the glass-fronted vending machines 10 using the prior art motor gearbox 20P of FIG. 3, a spiral 32 frequently becomes jammed by the item I if it fails to drop off the edge 12E of the shelf 12. The prior art electric motor gearbox 20P continues to run until the gearing fails in its output pinion 23 at its teeth 38 (see FIG. 7) before the minimotor 22 reaches its stall point.
Furthermore, if the prior art electric motor gearbox 20P of FIG. 3 does not fail in this manner, it eventually ceases to function because of "fatigue," i.e., constant starting and stopping of the minimotor 22 leads to failure. Also, since the gearbox housing 26 is somewhat flexible, intermittent vibrations contribute to hastening this failure.
Although U.S. Pat. No. 2,184,669, which issued to William L. Hansen on Dec. 26, 1939, suggests that a gear casing may have mated ribs on both the inside cover and the housing side thereof in order to provide "the utmost rigidity and freedom from vibration" (at page 2, col. 2, lines 24-27), such a gear casing is unsuitable for the specialized requirements of the food vending machine 10.
Consequently, as a result of such prior art failures, the disappointed purchaser would lose the money deposited, if no one was available to make a refund. Also, the merchant having the vending machine 10 would lose a sale and the snack food seller would have the machine 10 out of order for an undetermined length of time. Therefore, revenue would be lost for both the merchant and the food seller. Occasionally, the disappointed purchaser would become irate and vandalize the machine 10, thus causing greater losses for both the merchant and the food seller.
As a result, it has been a problem in the prior art to develop an electric motor gearbox that will cease functioning, but will not fail, thus preventing the disabling of the vending machine 10 when one of the items I becomes jammed and fails to drop from the shelf 12.